The present invention relates to an aqueous surfactant system suitable for use in a wide variety of subterranean reservoirs. More particularly, the invention relates to a particularly heat-stable and salt-tolerant aqueous anionic surfactant system (such as a petroleum sulfonate or other anionic surfactant system) containing a cosurfactant phenylethersulfonate which is capable of providing such tolerances while maintaining a high degree of interfacial activity.
U.S. Pat. No. 3,508,612 (issued more than a decade ago) describes a sulfate ester cosurfactant-containing aqueous petroleum sulfonate surfactant system which is particularly salt tolerant and capable of high interfacial activity at temperatures of less than about 150.degree. F. At higher temperatures the sulfate ester cosurfactants tend to be hydrolyzed to form less efficient alcohols at a rate which is undesirably high. U.S. Pat. No. 3,943,160 describes sterically hindered analogs of such sulfate esters which have both a similar efficiency as a cosurfactant and a greater heat stability within a subterranean reservoir. But, such homologs proved to be less attractive to manufacture and have failed to provide an economically attractive alternative cosurfactant for use in enhanced oil recovery processes. The disclosures of U.S. Pat. Nos. 3,508,612 and 3,943,160 are incorporated herein by reference.
The physical and chemical properties required for an effective cosurfactant are not predictable from the chemical structures of surface active compounds. Many surface active compounds are known to contain structural groups of the type needed for providing an affinity for both oil and water to an extent yielding at least some degree of surface activity as either or both a primary surfactant and/or a cosurfactant. Numerous types of such surface active compounds are described in U.S. patents.
For example, surface active compounds containing structural groups (which may be substituted groups) arranged as, (aryl)--(polyalkoxy)--(alkylethersulfonate), are described in U.S. Pat. Nos. 4,018,278; 4,161,218; 4,194,564; 3,203,491; 4,217,957; and 4,220,204.
Surface active compounds containing structural groups arranged as, (aryl)--(polyalkoxy)--(arylethersulfonate), are described in U.S. Pat. No. 3,977,471.
Surface active compounds containing structural groups arranged as, (alkyl)--(polyalkoxy)--(alkylethersulfonate) are described in U.S. Pat. No. 4,066,124.
Surface active compounds containing structural groups arranged as, (alkyl)--(polyalkoxy)--(arylethersulfonate) and their capability for increasing oil recovery when used in sea water by themselves or mixed with non-ionic surfactants are described in European Patent Application No. 60,079.
The cosurfactant compounds of the U.S. Pat. Nos. 3,508,612 and 3,943,160 mentioned above contain structural groups arranged as, (alkyl)--(polyalkoxy)--(alcohol sulfate ester).